The present invention relates to methods for testing integrated circuits, and more particularly to methods for testing packaged integrated circuits that have damaged or bent leads.
Integrated circuits (ICs) are typically tested during several stages of their lifetime. Testing is typically carried out by automatic test equipment (ATE) that includes an IC test signal generator (IC tester) and an interface tool (e.g., a probe card or a test socket). The interface tool is used to provide electrical connections to pads or leads of a device-under-test (DUT), and to route test signals between the DUT and the IC tester. This testing process is typically used to identify non-functional ICs, and is sometimes used to determine why the IC is nonfunctional.
FIG. 1 depicts an ATE arrangement that is utilized during wafer testing procedures performed before a wafer 100 is diced to form individual dies (IC chips) 110. Each die 110 includes circuitry (not shown) formed on the wafer material that is connected to pads 112 exposed on an upper surface of wafer 100. An IC tester 10 is used to apply test signals to pads 112 of each die 110 via a probe card 15-A that includes metal (e.g., tungsten) probes 17. Typically, wafer 100 is mounted on an X-Y table (not shown) that positions a selected die 110 under probe card 15-A. Metal probes 17 are then brought into contact with pads 112. Test signals are then transmitted between IC 110 and IC tester 10 via probe card 15-A. This wafer testing procedure identifies non-functional die on wafer 100, which are typically marked using ink or are otherwise identified (e.g., using wafer mapping).
After wafer testing is completed, wafer 100 is then cut (diced) to separate die 110 from each other. The nonfunctional die identified during wafer testing are discarded, and the good (functional) die are sent to a assembly facility for placement into various types of IC packages. The packaged ICs are then returned to the IC tester for operational verification.
FIG. 2(A) depicts an ATE arrangement that is utilized to test a packaged IC 200-A. As indicated, packaging involves housing each die 110 in a package body 210 (e.g., plastic) along with a series of metal leads 220 that contact pads 112 and extend from package body 210. The package type illustrated in FIG. 2(A) is a dual-in line package (DIP) in which leads 220-1 and 220-2 extend from opposite sides of package body 210 and are bent downward. For example, lead 220-1 includes a stub portion 220-1A extending from package body 210, and a terminal (arm) portion 220-1B extending downward from a shoulder (bend) 220-1C. During IC testing, arm portions 220-1B are inserted into a test socket 20 that includes a series of contacts 22 for passing test signals between die 110 and IC tester 10. After testing, good packaged ICs 200-A are sold to customers, and non-functional ICs are discarded.
ICs occasionally fail after passing all of the tests described above and are sold to customers. These failing parts are sometimes removed from the customer""s application and returned to the manufacturer so that the cause of failure can be determined. Unfortunately, many customers lack proper IC removal equipment and procedures, and the returned ICs often include bent or broken leads.
FIG. 2(B) shows a damaged IC 200-B in which lead 220-1B is bent inward at shoulder 220-1C such that arm 220-1B fails to align with the underlying contact 22 of test socket 20. In order to use test socket 20 to determine the cause of failure of damaged IC 200-B, it is necessary to manually bend arm 220-1B back into its original position. However, this repair process is very time consuming, and may not be possible if arm 220-1B breaks during the bending process. Therefore, the conventional process of testing damaged ICs using test socket 20 is very time consuming, and is sometimes impossible.
What is needed is a method for testing damaged ICs that avoids the problems associated with the prior art.
The present invention is directed to a method for testing packaged integrated circuits (ICs), and in particular to packaged ICs having damaged (e.g., bent) leads. According to the present invention, instead of attempting to re-bend or otherwise fix the damaged leads, a lower portion of each lead (whether damaged or not) is cut off such that only a stub of lead material is left that is located close to the package body of the IC. The IC is then mounted onto a probe card having upward-facing probes that contact the lead stubs. Test signals are then transmitted between an IC tester and the damaged IC through the probe card. By cutting (removing) the lower portion of each of the leads, a substantial amount of time is saved over prior art methods that require re-bending or otherwise repairing the leads so that the damaged IC can be tested using a test socket.
The present invention will be more fully understood in view of the following description and drawings.